A few years into filming the Fox drama, Barton, who was 17 when she was cast, began to get into some trouble. "We thought, 'Work hard, play hard,'" she tells People in this week's cover story. In late 2007, Barton was arrested and charged with DUI and possession of marijuana. "I really am disappointed in myself," she said at the time. "I don't intend to do something this stupid again."

Nearly two years later, police removed Barton from her L.A. home and took her to Cedars-Sinai Medical Center where she was under an involuntary 5150 hold after she threatened to kill herself. At the time Barton blamed it on wisdom tooth surgery, but now tells the magazine a different story. "It was a full-on breakdown... I was under enormous pressure." Barton says. "It was always, 'She's too skinny, she must be sick.' Then it was, 'She's too big.' I was never the right weight."